" The AWK Programming Language" is an extremely readable book and is required reading. Like AWK itself, this book is very concise (only 204 pages) with many many examples of awk scripts to play with.

The two other AWK books are more verbose, and somewhat assume that you have read the first book.

The two Tcl books have nothing to do with AWK, unless you plan to make (or modify) a graphical user interface for awkscripts, like Tclforawk.